Needle-shaped x-ray fluorescent material and method for vapor-deposition thereof on a substrate

ABSTRACT

In a method for vapor-depositing a substrate with a layer of a needle-shaped x-ray fluorescent material containing at least one alkali metal, alkali halogenide phases and an alkali halogenide are mixed in a vapor phase and are vapor-deposited on the substrate. A needle-shaped fluorescent material is thereby produced having the formula  
           (         (       M     ′   +       ⁢     H     ′   -         )     a     ⁢       (       M     ′′   +       ⁢     H     ′′   -         )       (     1   -   a     )         )     k     ⁢     :     ⁢           ⁢       (       M   x     ′   +       ⁢     S   y     z   +       ⁢     H   x     ′   -       ⁢     H       z   *     ⁢   y       ′′′   -         )     b     ⁢       (       M   x     ′′   +       ⁢     S   y     z   +       ⁢     H   x     ′′   -       ⁢     H       z   *     ⁢   y       ′′′   -         )     c     ⁢       (       M   x     ′   +       ⁢     S   y     z   +       ⁢     H   x     ′′   -       ⁢     H       z   *     ⁢   y       ′′′   -         )     d     ⁢       (       M   x     ′′   +       ⁢     S   y     z   +       ⁢     H   x     ′   -       ⁢     H       z   *     ⁢   y       ′′′   -         )     e         
 
wherein M +  is at least one metal ion from the group Na, K, Rb and Cs, H −  is at least one halogenide from the group F, Cl, Br and I and S z+  is at least one lanthanide ion from the group La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a method for vapor deposition of asubstrate with a layer of a needle-shaped x-ray luminophore with atleast one alkali metal as well as the x-ray luminophore itself. As usedherein x-ray luminophore scintillator with fluorescence as well asstorage luminophore with emission by stimulation with laser light.Fluorescence is generally understood as the excitation of a luminophorewith high-energy radiation (UV, x-ray) to cause emission of low-energyradiation (emission). In a storage luminophore, higher-energeticemission (for example 420 nm) is triggered with low-energetic radiation(for example 680 nm) since the “residual energy” in the x-ray has been“stored”.

2. Description of the Prior Art

X-ray luminophores are generally used in medical technology anddestruction-free material testing. In these applications, scintillatorswith spontaneous emission under x-ray excitation are used, as well asstorage luminophores with formation and storage of electrons and holeswith subsequent photo-stimulated emission (PSL) upon irradiation with,for example, red light are used. The x-ray luminophores based on analkali halogenide thereby assume a very particular role. Examples areCsl:Na in an x-ray intensifier, Csl:TI in a-Si detectors or, of late,CsBr:Eu as a storage luminophore plate as described in Proc. of SPIEVol. 4320 (2001), “New Needle-crystalline CR Detector” by Paul J. R.Leblans et al., pages 59 through 67.

In all cited medical applications of alkali halogenide it is common thata high x-ray absorption must ensue to achieve a high DQE in the alkalihalogenide layer, and the signal (light) must be clear over the noise. Ahigh x-ray absorption is achieved by an approximately 500-600 μm thickalkali halogenide layer. The problem of a still-too-low light yield isstill present in all cited medical applications. In particular the lowlight yield of the storage luminophore represents a problem that isstill not completely solved.

In U.S. Pat. No. 5,028,509, example 14 describes the use of CsBr:Eu as astorage luminophore, produced from CsBr and Eu₂O₃. The general formulafor the combination of the alkali halogenide luminophore (Cs and Br) isspecified as follows:(M_(1−x)M^(I) _(x))X.aM^(II)X′₂.bM^(III)X″₃: dB,whereby M=Cs or Rb, M^(I) is at least one alkali metal from the groupLi, Na, K, Rb and Cs, M^(II) is at least one bivalent metal from thegroup Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, M^(III) is at least onemetal from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Al, Ga and In, B is an activator that is at least onemetal from the group Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm,Y, Tl, Na, Ag, Cu, Mg, Pb, Bi, Mn and In, X, X′ and X″ are the same ordifferent and represent a halogen atom from the group F, Cl, Br and I.

Known from PCT Application WO 01/03156 A1 is a production method for astimulatable storage luminophore of the general formula CsX:Eu for thecombination of the luminophore for the Cs-bromide and/or -chloride. Sucha storage luminophore was produced from CsBr and EuBr₂, EuBr₃ or EuOBr.

European Application 1 113 458 describes a method is described forcoating a substrate in which Eu is introduced as EuX₂, EuX₃, and EuOX.

A common feature of all of these luminophores is that the dopingmaterial is a relatively simple molecule. These simple molecules areoften attached on interstitials.

In tests with storage luminophore powders, it has been shown thatmicroscopically small phases of the doping material can be formed in thealkali halogenide. In vacuum-deposited layers of CsBr:Eu, these phaseshave not been found before. This is due to the Eu concentration in thelayer being only maximally 3000 ppm (0.3 mol %), conditional uponproduction (different vapor pressures of CsBr and EuBr₂), while giventhe use of powder phases an optimal PSL signal was present only given Euconcentrations >1 mol %.

SUMMARY OF THE INVENTION

The invention is to fashion an x-ray luminophore as well as a method forproduction of a spicular x-ray luminophore, such that an optimal lightyield can be achieved.

The object is inventively achieved by a method wherein alkali halogenidephases are simultaneously vaporized with an alkali halogenide, mixed inthe vapor phase and vacuum-deposited on the substrate. The use therebyalready begins upon coating of the vaporizer with evaporating material.The vaporization of the phase not described in any of the literaturecited above; rather, a formation of the phase in the layer is described.

It has proven advantageous when the vaporization is implemented attemperatures between 50° C. and 300° C. and a pressure between 0.001 Paand 3 Pa.

A better distribution of the evaporated phases and increase of the lightyield is obtained when a temperature treatment of the luminophore layeris implemented after the vaporization and a cooling, whereby thetemperature treatment after cooling preferably ensues at roomtemperature in the presence of water vapor.

The temperature treatment inventively can ensue in the range of 100° C.to 300° C. in atmospheric air or an inert gas.

In an advantageous manner, Cs_(x)Eu_(y)Br_((x+2y)) can be used as analkali halogenide phase and CsBr can be used as an alkali halogenide,such that a x-ray storage luminophore of the general formulaCsBr:Cs_(x)Eu_(y)Br_((x+2y)) forms.

It has proven to be advantageous when a quantity x of the alkalihalogenide phase and a quantity (600 g−x) of the alkali halogenide aremutually vaporized.

The substrate, with the layer of the spicular x-ray luminophore,inventively can form a storage luminophore plate.

For inventive mixing, the alkali halogenide phase and the alkalihalogenide can be mixed in the vaporization phase and in a vaporizationboat, or the alkali halogenide phase and the alkali halogenide can beseparately introduced in a plurality of vaporization boats.

The object also is inventively achieved by an x-ray luminophore that itis produced according, to the above method, having the followingformula:((M^(′+)H^(′−))_(a)(M^(′′+)H^(′′−))_((1 − a)))_(k):  (M_(x)^(′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(b)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(c)(M_(x)^(′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(d)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(e)whereby M⁺ is at least one metal ion from the group Na, K, Rb and Cs, H⁻is at least one halogenide from the group F, Cl, Br and I and S^(z+) isat least one lanthanide ion from the group La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

Particularly advantageous is an x-ray storage luminophore according tothe following formula:CsBr:Cs_(x)Eu_(y)Br_((x+2y))

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is based on the concept of producing the alkali halogenidephases and vaporizing these simultaneously with an alkali halogenide.The vaporization can ensue from a vaporization vessel or from two ormore vaporization vessels. A temperature treatment of the storageluminophore, implemented after the vaporization and cooling, leads to abetter distribution of the evaporated phases and thus increases thelight yield by a factor of 2-10, typically by a factor of 4-5.

Tests have shown that the temperature treatment is effective only aftercooling to room temperature given simultaneous presence of water vapor.The water vapor can be added, for example, to an inert gas Ar, N₂, He,Ne, Kr or can be in atmospheric air. A direct high heating—also aftercooling after the vaporization—has as a consequence no improvement ofthe light yield. The layer must thus initially have been reposed towater vapor.

Needle-shaped layers that enable a homogenous distribution of the phasematerial in the alkali halogenide are created upon vaporizationconditional upon the pressure and temperature control. As a consequence,100- 800 ppm of the phase material (average value above the layerthickness) is already sufficient in order to achieve an optimal lightyield.

In vaporization, temperatures are set between 50° C. and 300° C. andpressures are set between 0.001 Pa and 3 Pa. The temperature givensubsequent tempering preferably is as high as the average substratetemperature was upon vaporization.

The tempering time is selected such that the desired light yield isachieved.

As a result of this mixture made from alkali halogenide and alkalihalogenide phase in the vaporization phase, a new spicular luminophoretype is produced that can be described with chemical formulas asfollows.

Via the formation of a phase Cs_(x)Eu_(y)Br_((X+2y)) in CsBr, a storageluminophore with very high light yield results of the combination:CsBr:Cs_(x)Eu_(y)Br_((X+2y)).

The general formula for the M⁺ alkali halogenides Na, K, Rb and Cs aswell as H⁻ halogenides F, Cl, Br and I reads:M′⁺H′⁻:M′⁺ _(x)Eu_(y)H′⁻ _(x)H″−_(2y), (also possible: . . .H″_(x)H′_(2y))whereby the halogenides H′⁺ and H″⁻ can be the same or different.

Two (or more) alkali halogenides can also be used as a matrix lattice;the general sum formula then reads:(M′⁺H′⁻)_(a) (M″⁺H″⁻)_((1−a)):M′⁺ _(x)Eu_(y)H′⁻ _(x)H′″⁻ _(2y),whereby the alkali halogenides M′⁺ and M″⁺ can be the same as well asdifferent. Likewise, the halogenides H′⁻, H″⁻ and H′″⁻ can be the sameor different.

According to the above configuration, other phases are also conceivable:(M′⁺H′⁻)_(a)(M″⁺H″⁻)_((1−a)):M″⁺ _(x)Eu_(y)H″⁻ _(x)H′″⁻ _(2y),and(M′⁺H′⁻)_(a)(M″⁺H″⁻)_((1−a)):M′⁺ _(x)Eu_(y)H′⁻ _(x)H′″⁻ _(2y)M″⁺_(x)Eu_(y)H″⁻ _(x)H′″⁻ _(2y),and generalized:(M^(′+)H^(′−))_(a)(M^(′′+)H^(′′−))_((1 − a)):  (M_(x)^(′+)Eu_(y)H_(x)^(′−)H_(2y)^(′′′−))_(b)(M_(x)^(′′+)Eu_(y)H_(x)^(′′−)H_(2y)^(′′′−))_(c)(M_(x)^(′+)Eu_(y)H_(x)^(′′−)H_(2y)^(′′′−))_(d)(M_(x)^(′′+)Eu_(y)H_(x)^(′−)H_(2y)^(′′′−))_(e)(or without H′″, only made of H′⁻, H″⁻), whereby a can be equal to 1, b,c, d and e can be equal to 0, and H′⁻, H″⁻ and H′″⁻ can be the same ordifferent.

Instead of Eu²⁺, other lanthanides S^(z+) from the group La, Ce, Pr, Nd,Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu can also be used. Thecorresponding general formula then reads:((M^(′+)H^(′−))_(a)(M^(′′+)H^(′′−))_((1 − a)))_(k):  (M_(x)^(′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(b)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(c)(M_(x)^(′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(d)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(e)The factor k can be 0, such that “pure” phase material is obtained.

Both scintillators (luminophores) and storage luminophores are containedunder the cited x-ray luminophores.

Some exemplary embodiments for production of the inventive luminophoreare subsequently specified:

-   a) 50 g CsEuBr₃ are mixed with 550 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   b) 20 g CsEu₂Br₅ are mixed with 580 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   c) 100 g CsEu₃Br₇ are mixed with 500 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   d) 10 g Cs₂EuBr₄ are mixed with 590 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   e) 10 g Cs₃EuBr₅ are mixed with 590 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   f) 100 g Cs₄EuBr₆ are mixed with 500 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   g) 30 g Cs₂Eu₂Br₆ are mixed with 570 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   h) 70 g Cs₃Eu₂Br₇ are mixed with 530 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   i) 35 g Cs₃Eu₃Brg are mixed with 565 g CsBr, and subsequently a    storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)) (spicular) is    produced with the typical vacuum-deposition method.-   j) 25 g CsEuBr₃ and 25 g Cs₂Eu₂Br₆ are mixed with 550 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   k) 15 g CsEuBr₃ and 25 g Cs₃Eu₃Br₉ are mixed with 560 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   I) 20 g CsEuBr₃ and 10 g CsEu₂Br₅ are mixed with 570 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   m) 10 g CsEuBr₃ and 40 g CsEu₃Br₇ are mixed with 550 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   n) 30 g CsEuBr₃ and 20 g Cs₂EuBr₄ are mixed with 550 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   o) 60 g CsEuBr₃ and 20 g Cs₃EuBr₅ are mixed with 520 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.-   p) 40 g CsEuBr₃ and 20 g Cs₃Eu₂Br₇ are mixed with 540 g CsBr, and    subsequently a storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y))    (spicular) is produced with the typical vacuum-deposition method.

Other mixtures made up of two materials of the CS2 . . . and CS2 . . .compounds and Cs₂ . . . and Cs₃ or Cs₄ . . . compounds—as have beenshown in the example Cs . . . —can also be used for production of thestorage luminophores. Other quantity, mixture and concentration ratiosof 0.1 mol % - 20 mol % are also suitable for the production of storageluminophore. Mixtures made from not only two materials, but rather madefrom three, four . . . materials are also suitable as a basis for astorage luminophore.

If a non-vaporizable residue remains in the vaporization boat, normallyCsBr:Cs_(x)Eu_(y)Br_((x+2y)) , pure CsBr can also be refilled andsubsequently this mixture can be vaporized. This can also ensue multipletimes until the CsBr: Cs_(x)Eu_(y)Br_((x+2y)) concentration has fallenunder 0.1 mol %.

Instead of a mixture, the individual substances Cs_(x)Eu_(y)Br_((x+2y))and CsBr can be vaporized from two or more vaporization boats. CsBr andCs_(x)Eu_(y)Br_((x+2y)) can also be vaporized as a mixture from onevaporization boat and be vaporized from a different one pure substance,for example CsBr.

A europium/bromine compound (for example EuBr₂, EuBr₃) can also bevaporized together with the Cs_(x)Eu_(y)Br_((x+2y)) and CsBr. Instead ofthe bromides, fluorides, chlorides and/or iodides can be used.

Europium oxybromides (for example EuOBr, Eu₃O₄Br, Eu₃OBr₄, Eu₄OBr₆) canalso be vaporized together with the Cs_(x)Eu_(y)Br_((x+2y)) and CsBr.Instead of the oxybromides, oxyfluorides, oxychlorides and/or oxyiodidescan also be used.

Europium oxides (for example EuO, Eu₂O₃) can also be vaporized togetherwith the Cs_(x)Eu_(y)Br_((x+2y)) and CsBr.

Europium oxybromide and europium oxide can also be vaporized togetherwith the Cs_(x)Eu_(y)Br_((x+2y)) and CsBr.

Instead of the specified cesium, other alkaline metals (Na, K, Rb) andall halogenides (F, Cl, Br, I) can be used in the mixtures correspondingto the illustrated general sum formulas.

By doping of an alkali halogenide with an alkali halogenide-rare earthphase, a needle-shaped luminophore type has been produced that issuperior to the known luminophore types in terms of its light yield.Depending on the luminophore combination, both scintillators and storageluminophores can be produced.

Although modifications and changes may be suggested by those skilled inthe art, it is the invention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

1. A method for vapor deposition of a substrate with a layer of aneedle-shaped x-ray luminophore with at least one alkali metal,comprising simultaneously vaporizing an alkali halogenide phase with analkali halogenide, mixed in the vaporization phase and vacuum-depositingthe vaporized material on the substrate.
 2. A method according to claim1, comprising implementing the vapor deposition at temperatures between50° C. and 300° C. and a pressure between 0.001 Pa and 3 Pa.
 3. A methodaccording to claim 1 comprising implementing a temperature treatment ofthe luminophore layer the vapor deposition and a cooling.
 4. A methodaccording to claim 3, comprising implementing the temperature treatmentafter cooling at room temperature in the presence of water vapor.
 5. Amethod according to claim 3 comprising implementing the temperaturetreatment in a range from 100° C. to 300° C.
 6. A method according toclaim 3 comprising implementing the temperature treatment in a mixtureof inert gas and water vapor.
 7. A method according to claim 3comprising implementing the temperature treatment in humid air.
 8. Amethod according to claim 1, comprising using Cs_(x)Eu_(y)Br_((x+2y)) assaid alkali halogenide phase and using CsBr as said alkali halogenide,to form an x-ray storage luminophore CsBr:Cs_(x)Eu_(y)Br_((x+2y)).
 9. Amethod according to claim 1 through 8 comprising simultaneouslyvaporizing a quantity x of the alkali halogenide phase and a quantity(600 g−x) of the alkali halogenide.
 10. A method according to claim 1,comprising mixing the alkali halogenide phase and the alkali halogenideand introducing the mixture into a vaporization vessel for vaporizationthereof.
 11. A method according claim 1 comprising separatelyintroducing the alkali halogenide phase and the alkali halogenide intorespective vaporization vessels and simultaneously vaporizing saidalkali halogenide phase and said alkali halogenide in the respectivevacuum vessels.
 12. A needle-shaped x-ray luminophore with at least onealkali metal, produced according to the method according claim 1 havingthe following formula:((M^(′+)H^(′−))_(a)(M^(′′+)H^(′′−))_((1 − a)))_(k):  (M_(x)^(′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(b)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(c)(M_(x)^(′+)S_(y)^(z+)H_(x)^(′′−)H_(z^(*)y)^(′′′−))_(d)(M_(x)^(′′+)S_(y)^(z+)H_(x)^(′−)H_(z^(*)y)^(′′′−))_(e)whereby wherein M⁺ is at least one metal ion selected from the groupconsisting of Na, K, Rb and Cs, H⁻ is at least one halogenide selectedfrom the group consisting of F, Cl, Br and I and S^(Z+) is at least onelanthanide ion selected from the group consisting of La, Ce, Pr, Nd, Pm,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.
 13. An x-ray luminophoreaccording to claim 12, comprising an x-ray storage luminophore havingthe formula:CsBr:Cs_(x)Eu_(y)Br_((x+2y)).